Thin film transistor array panel for liquid crystal display

ABSTRACT

Disclosed is a liquid crystal display capable of high quality image and bright display. Gate signal lines are curved at near switching elements of the liquid crystal display. A pixel area is defined by the gate signal lines and their intersecting data signal lines. Pixel electrodes and common electrodes are disposed along a longitudinal direction of a pixel. A pixel signal and a common signal line is connected to the pixel electrode and the common electrode respectively. A storage capacitor may be formed in the middle of a longitudinal direction of the pixel, or where generally a texture may arise during display. One half of the pixel may be symmetrical with the other half with respect to the storage capacitor. A common signal line may be parallel with the data signal line and be disposed nearer to the data signal line than a pixel signal line. The pixel may be disposed symmetrically with respect to the data signal line therebetween. The pixel shape may also be repeated in the direction of the gate signal line.

BACKGROUND OF THE INVENTION

(a) Technical Field

The present disclosure relates to a thin film transistor array panel fora liquid crystal display, and in particular, to a thin film transistorarray panel including two kinds of field-generating electrodes forgenerating horizontal electric field.

(b) Description of the Related Art

A conventional liquid crystal display (hereinafter LCD) using horizontalelectric field includes pixel electrodes and common electrodes forgenerating horizontal electric field. An LCD cannot display a highquality image when the behaviors of the liquid crystal molecules aredistorted, such as when the common electrodes and a common electrodeline connected to the common electrodes for transmitting a common signalare adjacent to each other, generally near a edge portion of a pixel. Awider black matrix may be used to cover the distorted portion of thepixel but it reduces aperture ratio and result in lower brightness ofthe display.

In addition, cross-talk coupling effect or electric field distortion,which generally occurs between adjacent current carrying lines andelectrodes such as between a data signal line and a pixel electrode or acommon electrode and a data signal line causes light leakage. Thus, inthe conventional technology a common electrode adjacent to the datasignal line is made with a width adequate to cover a region of thecoupling effect or field distortion. However, the wider coverage reducesthe aperture ratio.

Furthermore, since the common electrode or the pixel electrode extendparallel to the data signal line, generally along a longer lengthwisedirection of a pixel, the number of electrodes that can be placedthereto is limited.

SUMMARY OF THE INVENTION

It is an aspect of the present invention to provide a high quality imagedisplay, minimizing the effect from the distorted electric field ofimage signal in a liquid crystal display device.

According to one aspect of the present disclosure, a liquid crystaldisplay comprises; a substrate, a first signal line formed on thesubstrate and extending in a direction, a second signal lineintersecting but insulated from the first signal line, a first pixelelectrode formed in a pixel area defined by intersections of the firstsignal line and the second signal line, said first pixel electrodessubstantially parallel to the first signal line, a pixel signal lineconnected to the pixel electrode, a switching element connected to thefirst signal line, the second signal line, and the pixel signal line, afirst common electrode formed in the pixel area, said first commonelectrode parallel to said first pixel electrode, a common signal lineformed in the pixel area, said common signal line connected to saidcommon electrode, a first capacitor electrode formed in the pixel area,said first capacitor electrode connected to the pixel signal line, asecond capacitor electrode formed in the pixel area, said secondcapacitor electrode connected to said common signal line, a second pixelelectrode formed in the pixel area, said second pixel electrode oppositeto first pixel electrode with respect to said capacitor electrode andconnected to the pixel signal line, and a second common electrode formedin the pixel area, said second common electrode opposite to the firstcommon electrode with respect to said capacitor electrode and connectedto the common signal line, wherein said first signal line is curved atnear the switching element.

According to another aspect of the present disclosure, a liquid crystaldisplay comprises; a first signal line extending in a direction; asecond signal line, said second signal line parallel to the first signalline, a third signal line having a positive angle with respect to aperpendicular direction of the first signal line, said third signal lineintersecting the first signal line, a fourth signal line having anegative angle with respect to a perpendicular direction of the firstsignal line, said fourth signal line intersecting the first signal line,a pixel area having a first part, a second part and a third part, saidpixel area defined by the first, second, third and fourth signal lines,a first common electrode extending parallel to the third signal line,said first common electrode disposed in the first part of the pixel, afirst pixel electrode extending parallel to the third signal line, saidfirst pixel electrode disposed in the first part of the pixel area, asecond common electrode having a first line and a second line, saidfirst line parallel to the third signal line, said second line parallelto the fourth signal line and said second common electrode disposed inthe second part of the pixel area, a second pixel electrode having athird line and a fourth line, said the third line parallel to the thirdsignal line, said fourth line parallel to the fourth signal line andsaid second pixel electrode disposed in said the second part of thepixel area, a first capacitor electrode electrically connected to thecommon electrode, said first capacitor electrode disposed in said thesecond part of the pixel area, a second capacitor electrode electricallyconnected to the pixel electrode, said second capacitor electrodedisposed in said second part of the pixel area, a third common electrodeextending parallel to the fourth signal line, said third commonelectrode disposed in said third part of the pixel area, and a thirdpixel electrode extending parallel to the fourth signal line, said thirdpixel electrode disposed in the third part of the pixel area.

The pixel signal line overlaps the common signal line. The common signalline is parallel to the second signal line, which is disposed to thesecond signal line nearer than the pixel signal line disposed to theswitching element. It decreases the effect of electric field distortionarisen from a data signal line and enables to expand transmittable areawithin the pixel.

The first signal is curved at a positive or negative angle with respectto the perpendicular direction of the second signal line or a rubbingdirection on the substrate depending on a polarizing axis. It enables tomake a shape of the pixel trapezoid, echelon or others, which also helpto decrease or compensate the optical difference of a liquid crystal.The shape of the pixel area may be a rectangular or others. A storagecapacitor formed of the first capacitor electrode and the secondcapacitor electrode including a insulator interposed, is disposed in themiddle of a longitudinal direction of the pixel, or where a texture maybe formed during displaying. The capacitor electrode may be a shape oftriangle or other.

The first common electrode is disposed nearer to a gate signal line thanthe first pixel electrode. The second common electrode is also disposednearer to a gate signal line than the second pixel electrode. It alsodecrease the effect of electric field distortion arisen from the gatesignal line, which also improve an image quality and enables to expandthe transmissible area of the pixel.

The pixel area of the liquid crystal is repeated in a direction of thegate signal line expanding direction, or symmetrically with respect to adata signal line therebetween.

The pixel electrode and the common electrode may be disposed on the sameplanar place. The common electrode and the pixel electrode may have athickness of less than about 2000 Å.

The gate line may include a single film of such as Ag, Ag alloy, Al, Alalloy or their alloys. The gate line may also have a multi-layeredstructure including one of the above-described layers and/or one of apad layer.

The pixel electrode and common electrode may be formed of pluralparallelism of the two electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more apparent by describing preferredembodiments thereof in detail with reference to the accompanyingdrawings in which:

FIG. 1 is a schematic layout view of a thin film transistor (TFT) arraypanel for an LCD according to a first embodiment of the presentinvention;

FIG. 2 is a sectional view of the TFT array panel shown in FIG. 1 takenalong the line II-II′;

FIG. 3 is a sectional view of the TFT array panel shown in FIG. 1 takenalong the line III-III′; and

FIG. 4 is a schematic layout view of a TFT array panel for an LCDaccording to a second embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. The present invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein.

Thin film transistor (TFT) array panels for an LCD according toembodiments of the present invention will be described with reference tothe accompanying drawings.

A plurality of gate lines and a plurality of data lines, defining aplurality of pixel areas, are provided on a TFT array panel for an LCDaccording to the present invention. A plurality of common signal lines,connected to the common electrodes, extend parallel to the data lines orthe gate lines. In the absence of electric field liquid crystalmolecules are aligned perpendicular to the data lines or the commonsignals lines, and the gate lines extend parallel to the commonelectrodes.

A TFT array panel for an LCD according to a first embodiment of thepresent invention is now described with reference to FIGS. 1-3.

FIG. 1 is a schematic layout view of a pixel in a TFT array panel for anLCD according to a first embodiment of the present invention, and FIGS.2 and 3 are sectional views of the TFT array panel shown in FIG. 1 takenalong the lines II-II′ and III-III′, respectively.

Referring to FIGS. 1-3, a plurality of gate lines 121 extendingsubstantially in a transverse direction are formed on an insulatingsubstrate 110. The gate lines 121 may include a single film having lowresistivity such as Ag, Ag alloy, Al or Al alloy. The gate lines 121 mayalso have a multi-layered structure including one of the above-describedlayers and/or one of a pad layer having good contact characteristicswith other materials. An end portion of each gate line 121 transmits agate signal to the gate line 121 and a plurality of branches of eachgate line 121 constitutes a plurality of gate electrodes 123 of TFTs.The gate lines 121 intersect data lines and define a plurality of pixelareas. Preferably, the gate lines are slightly angled at or near thecurves of a pixel to form trapezoids.

Furthermore, a plurality of common electrode lines 138 and 132 areformed on the substrate 110. The common electrode lines 138 and 132extend in a longitudinal direction and parallel to each other. Aplurality of common electrodes 134 connecting the common electrode lines138 and 132 and extending parallel to the gate lines 121 are also formedon the substrate 110. The common electrodes 134 and the common electrodelines 138 and 132 are disposed at or near the edges of the pixel to formtrapezoids. A plurality of first storage capacitor conductors 136,connected to the common electrode lines 138 and 132 or the commonelectrodes 134 overlap a plurality of second storage capacitorconductors 176 connected to pixel electrodes, forming storage capacitorsin a central area of the respective pixel area. The common electrodes134 and the common electrode lines 138 and 132 are referred to as commonsignal lines hereinafter. The common electrodes may also be formedsymmetrically in a pixel. One half of the common lines may be parallelto a first gate line and a second half of the common lines parallel to asecond gate line, the first and second gate lines intersecting eachother, as shown in FIGS. 1 and 4. This structure is applicable to amulti-domain pixel as well as a multi-pixel unit.

A gate insulating layer 140 made of silicon nitride (SiNx) is formed onthe gate lines 121 and the common signal lines 132, 134, 136 and 138.

A plurality of semiconductor islands 150 made of hydrogenated amorphoussilicon (hereinafter a-Si) are formed on the gate insulating layer 140.A plurality of pairs of ohmic contacts 163 and 165, made of silicide orn+ a-Si heavily doped with n type impurity, are formed on thesemiconductor stripes 151. Each pair of ohmic contacts 163 and 165 areseparated with respect to the gate electrodes 123. The semiconductors150 and the ohmic contacts 163 and 165 may have a linear shape alongdata lines 171 or may have the same shape as the data lines 171 anddrain electrodes 175.

A plurality of data lines 171 and a plurality of drain electrodes 175are formed on the ohmic contacts 163 and 165 and the gate insulatinglayer 140. The data lines 171 and the drain electrodes 175 may include aconductive layer having low resistivity such as Al,Ag or its alloy. Thedata lines 171 extend substantially in the longitudinal direction andintersect the gate lines 121 to define a pixel area in various shapessuch as an echelon rectangular, trapezoidal, etc. A plurality ofbranches of each data line 171 extend onto the ohmic contacts 163 toform a plurality of TFT source electrodes 173. An end portion (notshown) of each data line 171 transmits image signals to the data lines171. The drain electrodes 175 are separated from the data lines 171 andlocated on the ohmic contacts 165 opposite the source electrodes 173with respect to the gate electrodes 123.

According to a preferred embodiment of the invention, a plurality ofpixel electrodes 174, a plurality of pixel electrode lines 172 and 178,and a plurality of second storage capacitor conductors 176 are formed onthe gate insulating layer 140. The pixel electrodes 174 extend oppositethe common electrodes 134. The pixel electrode lines 172 and 178 areconnected to the drain electrodes 175 and located near the edges of thepixel areas and overlap the common electrode lines 132 and 138. Thesecond storage capacitor conductors 176 are connected to the pixelelectrode lines 172 and overlap the first storage capacitor conductors136 to form storage capacitors. The pixel electrodes 174 and the pixelelectrode lines 172 and 178 are referred to as a pixel signal lineshereinafter.

A passivation layer 180 is formed on the data lines 171, the drainelectrodes 175, the pixel signal lines 172, 174 and 178, and the exposedportions of the semiconductor islands 150. The passivation layer 180 ispreferably made of silicon nitride or organic material having a goodflatness characteristic.

An alignment layer 11 for aligning liquid crystal molecules is formed onthe passivation layer 180.

A gate electrode 123, a source electrode 173, and a drain electrode 175along with a semiconductor island 154 and a pair of ohmic contacts 163and 165 form a TFT.

Although the common signal lines 132, 134 and 138 and the pixel signallines 172, 174 and 178 are formed of the same layer as the gate lines121 and the data lines 171, respectively, they may be on the same layer,for example, they may be located on the passivation layer 180. Thecommon signal lines 132, 134 and 138 and the pixel signal lines 172, 174and 178 preferably have thickness equal to or less than about 2,000 Å.This thickness presents alignment defect due to height difference.

Transverse arrows shown in FIG. 1 indicate a rubbing direction at thealignment layer 11 which is perpendicular to the data lines 171 or thecommon signal lines 132. The rubbing direction can be in directionsother than that shown by the arrows.

In a TFT array panel for an LCD according to the first embodiment thecommon signal lines 132 extend parallel to the data lines 171 along longedges of the pixel areas. The rubbing direction is also determined suchthat in absence of electric field the liquid crystal molecules arealigned perpendicular to the data lines 171. Accordingly, an electricfield generated by the voltage difference between the data lines 171 andthe common signal lines 132 orients the liquid crystal molecules totheir initial orientations. The corresponding areas are displayed darkto prevent lateral crosstalk. As a result, the common signal lines 132can be made to have a small width and aperture ratio can be increased.

In addition, since the common electrodes 134 and the pixel electrodes174 are arranged along a long edge direction of the pixel areas thenumber of the electrodes 134 and 174 and their positioning can be easilyvaried.

Furthermore, the effective display area can be enlarged to corners ofthe pixel areas because the pixel electrodes 174 or the commonelectrodes 134 located near the edges of the pixel areas extend parallelto the edges of the pixel areas defined by the gate lines 121 and thedata lines 171. Moreover, the storage capacitors are located near thecenters of the pixel area, where textures are generated so that they donot reduce the transmittance of the pixel areas, thereby maximizing thetransmittance of the pixel areas.

Although the above-described first embodiment arranges two adjacenttrapezoidal pixel electrodes in a row such that bottom edges or topedges of the trapezoids face each other as shown in FIGS. 1 to 3, abottom edge of a pixel area may face a top edge of an adjacent pixelarea in the row direction and vice versa, which is now described withreference to FIG. 4.

FIG. 4 is a layout view of a TFT array panel for an LCD according to asecond embodiment. The section view of the TFT array panel according tothe second embodiment is similar to that of the first embodiment of thepresent invention. The pixel areas, however, are repeatedly arranged ina row direction. That is, the adjacent pixel areas in a pixel row havethe same shape, while those shown in FIG. 1 have inverted or reversedshapes such that they are symmetrical with respect to a data linelocated therebetween.

As described above, the placement of the common signal lines and thedata in parallel along edges of the pixel areas and reduces lightleakage. In addition, the parallelism between the common electrodes andthe pixel electrodes or edges of the trapezoidal pixel areas extendsdisplay to the corners of the pixel areas, thereby maximizing displaycapacity of pixels. Moreover, the arrangement of the common electrodesand the pixel electrodes along a long edge direction of the pixelsfacilitates to a more varied placement the electrodes increases theaperture ratio.

While the present invention has been described in detail with referenceto the preferred embodiments, those skilled in the art will appreciatethat various modifications and substitutions can be made thereto withoutdeparting from the spirit and scope of the present invention as setforth in the appended claims.

1. A liquid crystal display, comprising: a substrate; a gate line formedon the substrate and extending in a first direction, wherein the gateline is bent at a positive or negative angle with respect to thedirection of a rubbing direction on the substrate; a data lineintersecting the first direction; a first pixel electrode formed in apixel area defined by intersections of the gate line and the data line,said first pixel electrode formed substantially parallel to the gateline; a pixel signal line connected to the pixel electrode; a switchingelement connected to the gate line, the data line, and the pixel signalline; a first common electrode formed in the pixel area parallel to saidfirst pixel electrode; a common signal line formed in the pixel areaconnected to said common electrode, wherein the distance between thecommon signal line and the data line is shorter than the distancebetween the pixel signal line and the data line; a first capacitorelectrode formed in the pixel area connected to the pixel signal line; asecond capacitor electrode formed in the pixel area connected to saidcommon signal line; a second pixel electrode formed in the pixel areaopposite to the first pixel electrode and connected to the pixel signalline; and a second common electrode formed in the pixel area, saidsecond common electrode opposite to the first common electrode andconnected to the common signal line, wherein at least the first orsecond capacitor electrode is triangular in shape.
 2. The liquid crystaldisplay of claim 1, wherein the pixel signal line overlaps the commonsignal line.
 3. The liquid crystal display of claim 1, wherein thecommon signal line is parallel to the data line.
 4. The liquid crystaldisplay of claim 1, wherein the gate line bends at a positive ornegative angle with respect to the perpendicular direction of the dataline.
 5. The liquid crystal display of claim 1, wherein the first commonelectrode is disposed nearer to the gate line than the first pixelelectrode.
 6. The liquid crystal display of claim 1, wherein the secondcommon electrode is disposed nearer to the gate line than the secondpixel electrode.
 7. The liquid crystal display of claim 1, wherein aplurality of pixel areas are provided disposed along, the direction ofthe gate line.
 8. The liquid crystal display of claim 1, wherein aplurality of pixel areas are provided disposed symmetrically withrespect to the data line therebetween.
 9. The liquid crystal display ofclaim 1, 7 or 8, wherein the pixel area is triangular in shape.
 10. Theliquid crystal display of claim 1, wherein the pixel electrode and thecommon electrode are disposed on the same planar plane.
 11. The liquidcrystal display of claim 1 or 10, wherein the pixel electrode and thecommon electrode have a thickness of less than about 2000 Å.
 12. Theliquid crystal display of claim 1, wherein the capacitor electrodes aredisposed in a longitudinal center of the pixel area.
 13. The liquidcrystal display of claim 1, wherein the first capacitor electrode is apart of the first pixel electrode.
 14. The liquid crystal display ofclaim 1, wherein the pixel area has a rectangular shape.
 15. The liquidcrystal display of claim 1, wherein the gate line is formed of at leastone material selected from a group of Al, Al-alloy, Ag, Ag-alloy and itsalloy.
 16. The liquid crystal display of claim 15, wherein the gate linefurther comprises a pad layer.
 17. The liquid crystal display of claim1, wherein a plurality of pixel areas are provided disposedpoint-symmetrically with respect to the gate line therebetween.
 18. Aliquid crystal display, comprising: a substrate; a gate line formed onthe substrate and extending in a first direction; a data lineintersecting the first direction; a first pixel electrode formed in apixel area defined by intersections of the gate line and the data line,said first pixel electrode formed substantially parallel to the gateline; a pixel signal line connected to the pixel electrode; a switchingelement connected to the gate line, the data line, and the pixel signalline; a first common electrode formed in the pixel area parallel to saidfirst pixel electrode; a common signal line formed in the pixel areaconnected to said common electrode; a second pixel electrode formed inthe pixel area opposite to the first pixel electrode and connected tothe pixel signal line; and a second common electrode formed in the pixelarea, said second common electrode opposite to the first commonelectrode and connected to the common signal line, wherein an outermostelectrode of the first pixel electrode, the pixel signal line and anoutermost electrode of the second pixel electrode join together to forma trapezoid shape.